Effect of protein binding with phytic acid on the thermal gelation of bovine serum albumin and canola 12S globulin at the intermediate pH range
Wong, Amy Wan-sau
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The present study was undertaken to examine how phytic acid interacted with canola 12S globulin at the intermediate pH range and to assess the effect of this interaction on thermal gelation. Bovine serum albumin (BSA) was used to form a model system to study the phytic acid binding to protein and its effect on thermal gelation. The degree of phytic acid binding was determined by using equilibrium dialysis as a function of pH and concentrations of phytic acid and calcium ion. Dynamic rheology was used to assess the influence of the binding on the thermal gelation under the same conditions. The phytic acid binding to BSA and the canola globulin was highly pH-dependent. The binding for both proteins was intensified at pH values below their isoelectric points and the highest binding was always at the lowest pH level regardless of the concentations of phytic acid and calcium. BSA gels formed at pH 5 were weak and inelastic due to the protein aggregation which was caused by the phytic acid binding and the proximity to the isoelectric point. Although the canola globulin gels formed at pH 5 and 7 (below the isoelectric point) were also weak and inelastic, the role of binding on thermal gelation was insignificant. The presence of calcium only decreased the binding of phytic acid to the canola globulin...The mechanism of phytic acid binding was found to be the electrostatic interaction between the negatively charged phytic acid and the positively charged residues on the proteins. This binding occurred at pH values close to and below the isoelectric point. There was no evidence to support the formation of a ternary complex (phytic acid-calcium-protein) at the pH values above the isoelectric point. As a result, only the gel structures formed at pH values below the isoelectric point were influenced by the phytic acid binding.